History of Chejudo Island Cheju is a volcanic island formed by activity from the 3rd Cenozoic period to the 4th period, 2 million years ago. It's assumed that Cheju of today was formed by the repeated change of state, being a part of continent and an island brought by volcanic activities, sea level changes from glaciation and crustal activity. You can see Bakroldam with its 700m diameter crater at the top of Halla mountain located in the center of island. It's assumed that people have lived in Cheju since prehistoric ages, on the basis of the remains found in Cheju City and Bukcheju-kun. The age of the country's foundation is not known, although there is a legend of three names telling that men named Ko, Bu, and Yang founded the country. There were tribal countries called Juho, Supra, Tammora and Tamra but were not big kingdoms or highly developed civilizations. After being a subject state of the three kingdoms of Paekche, Shilla and Koryo, Cheju island might have been called Tamla Gun under unfied Koryo in Sukjong 10(A.D.1105) and the name of 'Cheju' began to be used since Gojong 10 of Koryo (A.D. 1105). After that, Koryo was attacked by Won of China and the Sambeulcho (Name of army) resisted in Cheju. Therefore, Cheju has had a hard time of being ruled by Mongolia's general management department for 100 years in Wonjong 14(A.D.1273). Treated as an abandoned island, Cheju was used as banishment island for political scholars in the Chosun Dynasty. But progress of culture and spread of Confucianism was made thanks to these banished scholars such as Sonsiyuel, Kimjungho, ect. The only authentic book of Cheju, "Book of Tamra" was made in Hoyjong 4 (A.D.1653) and Cheju was promoted to Do (Province), separated from South Cholla-Do today after passing through the Japanese colonial period. The Cheju Information Network